The application of DTA and TG methods to investigate the non-crystalline hydration products of CaAl2O4 and Ca7ZrAl6O18 compounds

The hydration products and thermal decomposition mechanism of hydrated CaAl2O4 and Ca7ZrAl6O18 compounds were investigated by X-ray diffraction, SEM/EDS and thermal analysis. The processes of crystal hydrate nucleation and precipitation were preceded by the evolution of the X-ray amorphous phase during the first 24 h of hydration. DTA–TGA–EGA techniques allowed the study of the detailed decomposition and identification of intermediate and stable to be performed. The differential thermal analysis (DTA) curves of hydrated CaAl2O4 and Ca7ZrAl6O18 compounds show five similar endothermic peaks due to crystal water desorption. According to the quantitative TGA–EGA analyses performed on hydrated CaAl2O4 and Ca7ZrAl6O18 compounds, it was found that C2AH8, C3AH6 and Al(OH)3 phases are the main hydration products of CaAl2O4. Under the same laboratory conditions, the hydration of Ca7ZrAl6O18 proceeds with the formation of mainly CAH10 and AH3-gel phases. We provide the original illustrations of the hydrate crystals formation via amorphous phases.